According to the booklet "Boiler tubes facts", published by the Boiler Tube Company of America, the main boiler tubes standards are the following:
ASTM A-178: ER Welded Carbon Steel Boiler Tubes.
ASTM A-192: Sms Carbon Steel Boiler Tubes for High Pressure Service
ASTM A-213: Sms SS and Alloy Steel Boiler and Superheater tubes
ASTM A-249: Austenitic SS Boiler and Superheater Tubes.
According to these standards, boiler tubes are specified by the outside diameter and the minimum wall thickness. Of course, when you bend them, the wall thickness of the thinnest section (i.e., the convex side of the bend), must not be thinner than the specified minimum thickness. Therefore, you should select a wall thickness a little larger than the one you need, so it's able to take up this reduction in thickness.
As for ovality, the mentioned standards refer to ASTM A-450, which I didn't have time to read.
Giovanni S. Crisi